Current in a Loop: Solving for Magnitude at t=20s

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Homework Help Overview

The discussion revolves around a physics problem involving a loop with specific resistance, area, and turns, where participants are trying to determine the magnitude of the current at a given time based on magnetic flux and Faraday's Law.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning, Assumption checking

Approaches and Questions Raised

  • Participants discuss the need for additional equations and the relationship between magnetic flux, induced emf, and current. There is confusion regarding the use of a provided graph of magnetic field strength over time and how it relates to resistance and induced current.

Discussion Status

The discussion is active, with participants seeking clarification on the relationship between induced emf and current, as well as the implications of the slope of the B vs. t graph. Some guidance has been offered regarding the relationship between changing flux and induced emf, but confusion remains about specific terms and concepts.

Contextual Notes

Participants are working under a time constraint, as the homework is due soon, and there is a mention of a graph that is not shared visually in the thread. Some participants express uncertainty about terminology such as "ohmic."

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Homework Statement


This is the third part of a problem: The loop has a resistance of 0.20, an area of 200cm^2, and consists of 400 turns. What is the magnitude of the current in the loop at t=20s?


Homework Equations


Magnetic Flux=BAcos(theta)
Faraday's Law=-N(Magnetic Flux)/time


The Attempt at a Solution



I know I am missing an equation I need to figure this out but I'm not sure what it is. I have the N, A, t, and i have the resistance. I need to use the resistance to find the B, but I'm not sure how to do that. Please help. Thanks
 
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Are you given B(t)?
 
No so that's why I'm confused...in the first part of the problem it gives me a graph and at the time it says the B looks to be about -0.66 but I'm not sure if I'm supposed to use that or figure out the actual B using the resistance??
 
So you are given a graph of B versus t?
 
yes in the first part of the problem...i don't know how to insert pictures or i'd post that...for the time 20s it looks like it is -.66
 
Remember that the induced emf depends on the time rate change of the B field. What does that mean graphically?
 
Well I know the induced current is the slope of the line of the B vs t graph, but I'm not sure how to figure out what to do with the resistance for this part of the problem..??
 
candyq27 said:
Well I know the induced current is the slope of the line of the B vs t graph, but I'm not sure how to figure out what to do with the resistance for this part of the problem..??
No that is not quite right. The slope of B vs. t is a changing flux density (area density). Multiply it by the area to have the change in flux per time. Faraday found something out about this changing flux...
 
Ok now I'm really confused. I thought that the induced current was proportional to the negative slope of the magnetic flux graph..? Sorry if it's dumb, we just learned this tonight and have this homework due Wednesday so I'm trying to sort through it. Thanks for your help.
 
  • #10
The induced emf is proportional to the change in flux, here the area times the slope of the B vs. t, and I stress that works here.(Changing area is possible too)Now the loop is ohmic so that implies what?
 
  • #11
Is the induced emf the same thing as the induced current? We learned that the induced current is proportional to the neg slope of the graph. We also learned that the motional emf is -vLB. I don't know what ohmic is??
 
  • #12
candyq27 said:
Is the induced emf the same thing as the induced current? We learned that the induced current is proportional to the neg slope of the graph. We also learned that the motional emf is -vLB. I don't know what ohmic is??
Induced emf is not the same as induced current. The induced emf provides a potential which can move charge. How much moves? Well it depends; for an ohmic device the current is proportional to the voltage (emf). I will let you find out the proportionality constant.
The current is proportional to the slope for this problem, I wouldn't say that is a general statement.
Motional emf doesn't really apply here.
Google ohmic.
 

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